1. Field of the Invention
The present invention relates to a device and method for position detection on a plane surface selected by a user and providing the coordinate of the position to show information corresponding to the coordinate. In particular, the present invention relates to a position detection device that is able to detect positions on a plane surface of two dimensional with less conductive wires and more accurate detection results.
2. Description of the Related Art
A variety of technologies exist to determine the position of a stylus place on a surface. One technology is a grid of horizontal and vertical wires which placed below the surface of a flat tablet or over the surface of a display device such as computer monitors and providing position indicating signals which are selected by a stylus as shown in FIG. 1. One layer of wires 101 are separated by a grid pitch according to the resolution needed from Row 0 to Row N. Another layer of wires 102 with the same or different pitch forms Column 0 to Column M. Each wire is connected to a driving conductor, which connected to a wire select multiplexer. AC signal is applied to Row 0, Row 1, to Row N, sequentially. Two devices using this type of technology are described a U.S. Pat. Nos. 5/149,919 and 4/656,332 to Greenias, et al. These devices determine the position by applying a driving signal sequentially to a group of conducting wires will need very small grid pitch and more conductive wires to increase the accuracy; it also need more driving conductor to drive the conducting wire. The mechanical and electrical complexity necessary to make the connection would be prohibitive. Although one of them had made use of grouping technology to the wires, the accuracy is still limited. When the AC signal is applied to Row k, all the other rows are kept at zero potential (i.e. at ground voltage). The AC signal is then detect by a capacitive coupling device such as a stylus. By the time the signal is detected, the position of row of the detecting device is determined. After the position is determined, AC signal is then applied to the Columns and using the same device to detect the signal. The position of column can also be determined.
In another technology as shown in FIG. 2, a conductive material layer 200 having electrical resistivity and three or four space apart contact points 201 electrically interconnected with the layer. When signal is applied to each contact, the selected position is determined by the signal received from the stylus and calculated by a processor. Two devices using this type of technology are described in U.S. Pat. Nos. 5/877,458 and 5/686,705 to David J. Conroy and Mark Flowers. These devices determined the position by measuring the unique position indicating signals and compare to that location information stored in the memory. These devices need only 4 to 5 conducting wire (one for stylus). It needs a very uniform resistive thin film 200 over a substrate for each system, which needs very accurate deposition technique to accomplish the mass production. After deposition, it also requires adjusting the location information or parameter for each system; it still needs a very accurate A/D converter to insure the measured signal is accurately converted to position coordinate.
What is needed is an improved method and system for position detection with less conductive wires and more accurate position information. It also need not use expensive and very accurate method to manufacture the device.